Recently, in apparatus associated with magnetic recording, such as video tape recorders (VTRs), hard disk devices (HDDs) or floppy disk devices (FDDs), it has been attempted to raise the recording density of recording signals. To this end, a hard magnetic material exhibiting high coercivity and high residual magnetic flux density is employed as a magnetic material of the magnetic recording medium. Thus it has become necessary to use a soft magnetic material having a higher saturation magnetic flux density and a high magnetic permeability than heretofore as a soft magnetic material which is employed in a magnetic head adapted for writing magnetic recording signals on the magnetic recording medium.
For this reason, a composite magnetic head having a magnetic core of the type in which thin films formed of a magnetic metal material of a high saturation magnetic flux density are deposited on core blocks formed of an oxide magnetic material, such as ferrite, and thus exhibiting both the high saturation magnetic flux density and the high magnetic permeability, has come into use in place of conventional ferrite magnetic heads having a low magnetic flux density.
However, with the composite magnetic head, also known as a metal-in-gap (MIG) head, a reaction layer or diffusion layer is formed on the interface between the ferrite core and the soft magnetic metal material during heating to a higher temperature, such as during crystallization heat treatment of the soft magnetic film or glass fusion, indispensable in the manufacture process of the magnetic head, thus resulting in markedly lowered magnetic properties as the soft magnetic material in the reaction layer. Thus the reaction layer acts as a pseudo magnetic gap independently of the normal magnetic head.
When the composite magnetic head is used as a magnetic head for signal reproduction, the pseudo magnetic gap, formed parallel to the normal magnetic gap, deteriorates the quality of reproduced signals. That is, due to interference with pseudo signals emanating from the pseudo magnetic gap, the reproduced signals exhibit wavy frequency (beat) characteristics having alternate crests and valleys, as shown in FIG. 5. The magnitude of waviness is expressed as a ratio in dB of the crests to the valleys of the output signals in the frequency characteristics shown in FIG. 5. The presence of the pseudo magnetic gap presents a serious problem because, if the magnitude of the waviness exceeds 1 dB, the composite magnetic head having such playback signal output can no longer be used practically for reproducing magnetic recording.
For obviating such problem, the JP Patent KOKAI publication No. 1-100714 (1989) discloses a composite magnetic head in which the reaction inhibiting layer containing an oxide(s) of Si, Ti, Cr, Al or the like is formed to a thickness of 2 to 20 nm in the boundary surface of the two magnetic materials.
However, it has been known theoretically that the magnitude of the waviness (beat) in the pseudo magnetic gap is a function of the ratio between the thickness of pseudo magnetic gap and the gap length of the normal magnetic gap (IEEE article, 0018-9464/84/0900-872S01.00, .COPYRGT. 1984). Therefore, the thickness of the reaction inhibiting layer in the above mentioned Kokai Publication, acting as the pseudo gap, needs to be defined in connection with the gap length of the normal magnetic gap. However, in the composite magnetic head of the above mentioned Kokai Publication, no reference is made to this point in determining the thickness of the reaction inhibit layer.